Playground: QuestDB version is stale

The playground's QuestDB VM runs 9.3.1, but the examples it serves come from the current repo, which needs 9.3.2+. Two entries in its own Example dropdown fail:

```
$ curl -sS -X POST 'https://clickbench-playground.clickhouse.com/api/query?system=questdb' \
--data-binary "SELECT length_bytes('abc');"
{"error":"unknown function name: length_bytes(STRING)","position":7}

$ curl -sS -X POST 'https://clickbench-playground.clickhouse.com/api/query?system=questdb' \
--data-binary 'SELECT build();'
Build Information: QuestDB 9.3.1, JDK 17.0.9, Commit Hash 5480b2d313653b591403df4c924a84ed9fcd6703
```

Q28 and Q29 use `length_bytes()`, which first shipped in [9.3.2](https://github.com/questdb/questdb/commit/667eefc340f5d0365d84075d885a8ecdc362ec28). `questdb/install` has pinned 9.3.5 since #902; the snapshot predates that merge. (Reverting the queries to `length()` isn't the fix - URL and Referer aren't ASCII, so it would shift those answers by 2.8% and 5.1%.)

Fix:

```
curl -X POST http://localhost:8000/api/admin/provision/questdb
```

## It will come back

`handle_queries` reads `queries.sql` from the repo checkout on the host, but the engine answering comes from a snapshot built when the system was first provisioned. `provision-all.sh` skips anything already snapshotted, and INSTALL.md documents re-provisioning only after **agent** or **base-image** changes. So `git pull && provision-all.sh` picks up new systems and never refreshes changed ones.

Nine systems pin an explicit version; five report live exactly what the repo pins. That's less reassuring than it looks - those five pins were last touched 2026-05-07..05-15, before provisioning, so they've had no chance to drift. QuestDB is the only one whose pin moved afterwards, and it's the one that drifted.

49 systems have had `install`/`create.sql`/`queries.sql`/`load`/`start` changes since 2026-05-20. Which of those predate their snapshot is visible to you and not to me.

I drafted a staleness check in #1145 - fingerprint each system's scripts at provision time, expose `source_stale`, let `provision-all.sh` re-kick the stale ones. Closed it since this is your infrastructure and you may want a different shape, but happy to revive.